An antenna device including a primary radiator, a main-reflector, and a sub-reflector has been used. Such an antenna device needs to be strong enough for outdoor use. Further, such an antenna device needs to have a low side-lobe characteristic according to the use.
For example, Patent Literature 1 discloses an antenna device including: a side plate in the form of a cylindrical shell attached to the outer circumference of a main-reflector, a housing in the form of a truncated cone shell that accommodates a part or the whole of a sub-reflector and a primary radiator and is attached to the side plate; and a reinforcement shell formed by a part of a conical shell attached to the left/right sides of the side plate and the housing. With this configuration, the antenna device has a high strength. Further, a corrugated horn antenna may be used as the primary radiator for such an antenna device in order to achieve a low side-lobe characteristic. The corrugated horn antenna includes bellows-like protrusions on its inner wall surface, and these bellows-like protrusions can lower the side-lobe.